import math,string,itertools,fractions,heapq,collections,re,array,bisect,sys,random,time,copy,functools
sys.setrecursionlimit(10**7)
inf = 10**20
mod = 10**9 + 7
def LI(): return [int(x) for x in sys.stdin.readline().split()]
def LI_(): return [int(x)-1 for x in sys.stdin.readline().split()]
def LF(): return [float(x) for x in sys.stdin.readline().split()]
def LS(): return sys.stdin.readline().split()
def I(): return int(sys.stdin.readline())
def F(): return float(sys.stdin.readline())
def S(): return input()
class Ruiwa():
def __init__(self, a):
self.H = h = len(a)
self.W = w = len(a[0])
self.R = r = a
for i in range(h):
for j in range(1,w):
r[i][j] += r[i][j-1]
for i in range(1,h):
for j in range(w):
r[i][j] += r[i-1][j]
def search(self, x1, y1, x2, y2):
if x1 > x2 or y1 > y2:
return 0
r = self.R
rr = r[y2][x2]
if x1 > 0 and y1 > 0:
return rr - r[y1-1][x2] - r[y2][x1-1] + r[y1-1][x1-1]
if x1 > 0:
rr -= r[y2][x1-1]
if y1 > 0:
rr -= r[y1-1][x2]
return rr
def main():
h,w = LI()
a = []
for i in range(h):
t = LI()
a.append([t[j] if (i+j)%2 == 0 else -t[j] for j in range(w)])
rui = Ruiwa(a)
r = 0
for i in range(h):
for j in range(w):
for ii in range(i,h):
for jj in range(j,w):
if rui.search(j,i,jj,ii) == 0:
t = (ii-i+1) * (jj-j+1)
if r < t:
r = t
return r
print(main())